The present invention relates to a digital signal repeater for repeating digital signals and, more particularly, to a repeater of the type including a controller for controlling the activation of a radio transmitter.
A repeater of the type described generally includes a radio receiver, a radio transmitter, and a controller. The receiver receives a modulated wave which has been transmitted from a terminal station or the like and demodulates the wave to provide a digital signal. The transmitter retransforms the digital signal into a modulated wave which is sent to another terminal station or the like. The controller controls the operation of the transmitter such that: (1) while a modulated wave is being received, the transmitter is activated (turned on) and retransmits (repeats) the modulated wave; and (2) while a modulated wave is not being received, the transmitter is not activated (turned off) so as not to retransmit a modulated wave. Whether or not a modulated wave has been received may be determined by detecting the level of a modulated wave in the intermediate frequency (IF) band of the receiver.
However, this approach has the drawback that the IF band modulated wave level sometimes reaches a sufficient value in response to the reception of an interference wave from another system is (rather than the modulated wave itself), thereby undesirably activating the transmitter to repeat the interference signals.